Synthesis of Rhodium and Iridium Complexes Supported by Bis(indolylphosphino)silyl Pincer Ligation: Competitive N–H and C–H Bond Activation by an Ir(I) Species

Abstract

The synthesis of five-coordinate amido hydride PSiP pincer complexes of both RhIII and IrIII was pursued. The preparation of such complexes by a salt metathesis route was initially targeted to assess the synthetic viability of such species. Isolable anilido hydride complexes of both Rh and Ir proved accessible, and rare examples of thermally robust Ir alkylamido hydride complexes were found to be viable synthetic targets. The preparation of amido hydride species by N–H oxidative addition was also pursued. Toward this end, the generation of coordinatively unsaturated ( i Pr-PSiPInd)­MI (M = Rh, Ir) species was investigated. Dehydrohalogenation of ( i Pr-PSiPInd)­RhH­(Cl) (1) under N2 afforded the isolable complex [( i Pr-PSiPInd)­Rh]2(μ-N2) (8a). While the N2 ligand could be displaced to afford ( i Pr-PSiPInd)­RhL (L = PMe3, DMAP, H2NPh), such RhI species proved unreactive toward N–H oxidative addition of aniline. Dehydrohalogenation of ( i Pr-PSiPInd)­IrH­(Cl) (2) in benzene solution resulted in activation of the solvent to afford ( i Pr-PSiPInd)­IrH­(Ph) (11), which undergoes facile arene exchange with benzene-d 6. In cyclohexane solution, treatment with aniline afforded a mixture of N–H and aniline sp 2-C–H bond oxidative addition products, with the latter species being favored. Although the observation of arene exchange involving ( i Pr-PSiPInd)­IrH­(Ph) suggests that C–H bond oxidative addition is reversible, attempts to drive the reactivity with aniline in the direction of N–H bond oxidative addition were unsuccessful. This reactivity differs significantly from that of previously reported complexes supported by related PSiP ligation. Most notably, it appears that for ( i Pr-PSiPInd)­Ir, products resulting from N–H- and C–H-oxidative addition of aniline substrates do not readily interconvert, although both are postulated to share a common intermediate of the type ( i Pr-PSiPInd)­Ir­(NH2Ph).

Stereodivergent asymmetric synthesis of P-atropisomeric Si-stereogenic monohydrosilanes

“…With a library of P-atropisomeric Si-stereogenic monohydrosilanes in hand, preliminary synthetic derivatizations of these hybrid chiral BINEPINE-based hydrosilanes were investigated. Given the significance of achiral silyl ligands or silyl metal complexes in catalysis, 11 the synthesis and characterization of chiral metal–silicon complexes were conducted, which had not been explored previously (Fig. 4a and b).…”

Tetrelanes versus Tetrylenes as Precursors to Transition Metal Complexes Featuring Tridentate PEP Tetryl Ligands (E=Si, Ge, Sn)

“…PSiP silyl complexes of Rh, [54] Ir, [54] Ni, [55] Pd [55] and Pt [55] have been recently prepared from bis(indolyl)silane D (Scheme 2), reacting it with [M 2 Cl 2 (cod) 2 ] (M=Rh, Ir), [NiCl 2 (dme)], [Pd 2 Cl 2 (allyl) 2 ] and [PtCl 2 (SEt 2 ) 2 ], respectively (Scheme 2). Silane D was synthesized in several steps from 3‐methylindole: a) n BuLi, b) CO 2 , c) t BuLi, d) P i Pr 2 Cl e) H 2 O, f) n BuLi and g) 0.5 SiCl 2 MeH [55,56] .…”

“…[44b] Many complexes derived from silanes of type C are efficient catalyst precursors for alkene hydrosilylation, [15,38] carbonyl group hydrosilylation, [33,40b] alkene hydrogenation, [20,24,44a] alkyne hydrogenation, [20] dinitrogen silylation, [9,25,38,52] silane deuteriation, [50] organic azide carbonylation, [13] allene carboxylation, [31,36d,f] CO 2 hydroboration, [31,32] alkene isomerization, [32] alkene dehydrogenative borylation, [36a,b] sila-Negishi coupling, [39a] ketone transfer hydrogenation, [21,34,40a] 2butyne isomerization and dimerization [53] and arene borylation. [27] PSiP silyl complexes of Rh, [54] Ir, [54] Ni, [55] Pd [55] and Pt [55] have been recently prepared from bis(indolyl)silane D (Scheme 2), reacting it with [M 2 Cl 2 (cod) 2 ] (M=Rh, Ir), [NiCl 2 (dme)], [Pd 2 Cl 2 (allyl) 2 ] and [PtCl 2 (SEt 2 ) 2 ], respectively (Scheme 2). Silane D was synthesized in several steps from 3-methylindole: a) nBuLi, b) CO 2 , c) tBuLi, d) PiPr 2 Cl e) H 2 O, f) nBuLi and g) 0.5 SiCl 2 MeH.…”

Synthesis of pyrrole-based PSiP pincer ligands and their palladium, rhodium, and platinum complexes

“…8,10 Variation of the linkers in PSiP ligands has been less explored, particularly regarding 1,2-arylene groups, which encourage preorganization; to our knowledge, only indole-based linkers have been incorporated (( iPr P In ) 2 Si) . 12,14 Due to this dearth of alternative linkers, the steric and electronic effects of changing arylene linkers for PSiP complexes have not been systematically studied.…”